As explained in U.S. Pat. No. 4,053,052, a hospital pharmacist frequently adds supplemental medication to an intravenous solution container which has a sealed closure. This patent describes attaching a protective outer cap by means of adhesive for protecting the inner closure during transport from the pharmacy to the operating room or patient's room. Since such outer cap is primarily a dust cover, it need not have the liquid sealing characteristics of the container closure.
The main liquid tight closure of a container often has a cumbersome structure requiring massive screw assembly machines, plastic fusion machines, etc. to insure that an adequate seal has been made in a liquid tight manner on a container for sterile medical solution for introduction into a patient's vein or into a surgical wound. U.S. Pat. No. 3,110,411 shows a threaded screw cap that uses the threaded mechanical advantage to forcibly wedge a stiff snap ring onto a neck flange of a container. The snap ring is preassembled to the screw on cap so the threaded cap can force it in place. It would be burdensome for the pharmacist to manually screw on such closures on a large number of containers to which additive medication is added each day. The various embodiments of this patent have structures indicating this closure is intended to be applied with machinery at the site of manufacture. It would not be well suited for manual assembly in a pharmacy.
Another type of closure suited only for application by a manufacturer is shown in FIG. 7 of U.S. Pat. No. 3,205,889. Here heat fusion type sealing equipment is necessary to seal retaining ring material to a container (plastic bag).